In 3rd Generation Long Term Evolution (3G LTE), a total of 504 cell identifiers are defined, and the 504 cell identifiers are divided into 168 cell identifier groups. Therefore, three cell identifiers exist in each cell identifier group. A downlink frame for 3G LTE includes two synchronization channels, that is, a primary synchronization channel and a secondary synchronization channel. The primary synchronization channel provides 5 msec-timing and information on three cell identifiers in the cell identifier group to a terminal. Accordingly, three primary synchronization channel sequences are used in the LTE system, and the primary synchronization channel sequences transmitted in a cell are equal to each other at each location of primary synchronization channel symbols. Since the secondary synchronization channel provides information on the cell identifier group and 10 msec-frame timing to the terminal, the secondary synchronization channel sequences transmitted from the location of two secondary synchronization channel symbols in the 10 msec-frame are different from each other. Therefore, the number of secondary synchronization channel sequences becomes 336 (=168*2).
FIG. 1 is a view illustrating a method of generating a secondary synchronization channel symbol according to the conventional art. As shown in FIG. 1, the secondary synchronization channel symbol according to the conventional art is an OFDM signal in which two short binary sequences are combined to each other in a frequency domain, thereby providing cell group information and frame boundary information to the terminal. The length of the binary sequences is 31, and the number of binary sequences is also 31. Ultimately, the number of sequences (62 in length) of the secondary synchronization symbol that can be generated as a pair of binary sequences is 961 in total, and only 336 sequences of these are used.
In the 3G LTE technique, four short binary sequences are used during a 10 msec-frame interval. At this time, the four short binary sequences may be different from one another or may be equal to one another, and four short binary sequences are provided to every cell by the cell group identifier. It can use at least one same sequence or two same sequences among four short binary sequences between adjacent cells, particularly between adjacent cells when 10 msec synchronization of two cells match with each other. In this case, interference between adjacent cells largely operates during a cell search process in the terminal, and performance can be significantly deteriorated.